Electric indicating apparatus



y 1, 1951 K. T. KALLE 2,551,008

ELECTRIC INDICATING APPARATUS Filed May 6, 1948 INVENTOR H IarL folJlell/lfdlle ATTORNEYS Patented May 1, 1951 UNITED;

STATES PATENT? OFFICE Application May 6, 1948, Serial No. 25,427 In Sweden October 24', 1945 2 Claims.

The presentinvention refers to an improvement of an arrangement for the remote indication of steam pressure, temperature, of a type known from a previous patent to the same inventor (Swedish Patent No. 67,175) The known arrangement operates in such a manner that the magnitudeto be measuredthrough some suitablemeans, .is. allowed to act upon one of the contactsin a contact device whose other contact is actuated. by a heating wire; The current which the contact device switches off and on in dependence of the magnitude'to bemeasured and of the temperature of theheating wire flows through the heating wire and istransmitted to the distant indicating device. The effective value of the current pulses thus produced-constitutes the measure of the magnitude to be measured.

Owing to the fact that the heating wire must have the required physical strength and consequently a fixed minimum area, its electrical resistance will be small so that the current intensity will have to be relatively great in order to obtain the required rapid heating of the heat.-. ing wire. If, as in arrangements hitherto known, thecontact device is included in the same circuit as the :heating wire, the contact has then to interrupt this entire current intensity which readily gives rise to arcs so that the, contacts become burned. Furthermore, because of the low resistance of the heating wire, only a low voltage can be applied to the circuit. This involves the drawback. that variations in'contact resistance due toburns or the like affect the current intensity to a high degree.

In accordance with the present invention, therefore, an arrangement is proposed, wherein the contact device in series with the source of current is connected in circuit with the primary winding (high tension windingl of a transformer and wherein the heating wire is connected in the measuring circuit in series with the secondary winding (low tension winding) of the transformer.

Also, a form of execution is proposed, wherein the primary of the transformer is provided with a center tap and wherein the contact device in series with the source of current is connected to one of the halves of the primary, whose second half in series with a condenser for extinguishing the arc between the contacts at the breaking operation is in parallel with the breaking point of the contact device andwith the series connection of said first half of the primary and the source of current.

The advantage with the arrangement according to the invention-is that the secondary ofthe transformer supplies the required heavy cur-- rent but a low voltage, while the primary in series with the contactdevice may be connected to, the A. C. mains, that is to a relatively high voltage so that the current intensitybecomesless for-the same effect as in the secondary.

With the present arrangement it is possible to maintain the voltage high and the current intensity low in the contactcircuit and ;simul-' tanecusly-therewith to obtain a current ofthe proper intensitythrough-the heating wire.;

In the figure of the accompanying drawing there is shown by way of example an embodiment of the invention. One of the conductors I from an A. C. source of current is connected to one of the halves 9 :of the primary winding 9, it of a transformer 9; Ill, [2 and the other conductor 4 is connected to one of the contacts 3 of the contact device, The center tap of the primary is connected with the other contact 4 of the contact device through the conductor 8.

The second half. it ofthe primary in series with a condenser i l is disposed in parallel to the contacts 3, i. The contact 3 is actuated by a Bourdon tube 2 "communicating with a boiler (not shown) or the like, the steam pressure of which is to be measured, and'the contact 4 is carried in a support I4 by means of a spring 5. A heating wire 5 is clamped in the support I 4 and is kept stretched by the spring 5; The wire 6 is included in a circuit, fed by the transformer 9, it), 12- and comprising: the secondary H, a conductor -i5,the spring 5, the .wire 6,. a conductor t6, the primary of a transformer 13 and a conductor H. The secondary of the transformer IL! feeds an indicating instrument comprising two metal springs l8 and IS, an electrically conducting bridge 28 joining the springs I8, IS, a hand 2! and a scale 22. When the same current flows through the springs l8 and I9, they become heated but dilate differently so that when clamped as shown they function as a bimetal. The curvature of the springs and hence the position of the hand 2| constitutes the measure of the effective value of the current flowing through the springs.

In order to explain the operation of the arrangement it is assumed that a certain pressure exists in the Bourdon tube 2 so that it has straightened itself to a certain degree and that the contacts 3, 4 are closed for the moment so that the transformer winding 9 is connected to the A. C. source. In the transformer winding there is produced a current which flows through the heating wire 6 and in so doing heats said. wire. Owing to the thermal expansion thereof and the action of the spring the contact 4 is brought downwards causing a breaking of the contact engagement. The condenser H in series with the transformer winding It] prevents the formation of possible arcs between the contacts. When the primary current in the transformer is interrupted, its secondary current ceases too, in consequence of which the wire 6 is no longer energized and begins to cool down and contract. When the wire 6 has resumed its original length, the contacts 3 and 4 are remade and the same process will be continually repeated as long as the pressure in the tube 2 remains constant. The alternating current pulses produced by the breaking and closing of the contacts pass through the transformer 13 and the springs 18 and I9, which are heated by the current and then, as stated above, bend so that the position of the hand 2| corresponds to the effective value of the current. At a uniform pressure in the tube 2 the periods of closed contacts are obviously of the same length of time and also the periods of open contacts. The efiective value of the current pulses and hence the position of the hand 21 thus becomes constant at a constant pressure. If the pressure increases, the tube 2 will have time to straighten itself a little, while the contacts are open, and therefore the contacts 3 and 4 will be remade before the wire has resumed its former length. At the same time, as the minimum temperature of the wire 6 must be higher in order that its new minimum length will correspond to the new position of the contact 3, the heat emission from the wire to the surroundings becomes greater owing to higher temperature of the wire. Consequently, the periods of closed current become longer and the intervals between them become shorter at the state of equilibrium for the new pressure. Thus, the eiiective value of the current and hence the deviation of the hand 2! becomes greater.

Other embodiments of the invention are possible within the scope of the claims. Thus, the arc may be extinguished by means of a resistor and a condenser respectively in series and in parallel with the contacts.

What I claim is:

1. An electric indicating apparatus comprising a current source and conductors leading therefrom, a transformer having a primary and a secondary winding, said secondary winding comprising the low tension winding of said transformer, one said conductor being connected to the primary winding of said transformer, a contact device, said contact device including a pair of contacts, a member dependent on the magnitude to be measured carrying one said contact, said contact carried by said member being connected to a second said conductor from said source, a spring carrying the second of said contacts, said second contact being connected to the primary winding of said transformer, a thermoresponsive heating wire connected to the secondary winding of said transformer and to said spring carrying said second contact, a measuring element connected in series with said heating wire said secondary winding, the position of one of said contacts being dependent on the magnitude to be measured and the position of the other contact carried by said spring being dependent on the variations in length of the heating wire for controlling the opening and closing of the contact device, the measure of the magnitude to be measured being the effective value of the current pulses produced by the opening and closing operations of the contact device fed to the heating wire.

2. In an electric indicating apparatus as claimed in claim 1, a center tap connecting the said contact device in series with the source of current to one-half of the primary of said transformer, a condenser connected in series with the second half of said primary winding and in parallel to the breaking point of said contact device and the series connection of said first half of said primary winding and said source of current.

KARL TORSTEN KALLE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,899,670 Chromy Feb. 28, 1933 1,969,719 Beck Aug. 14, 1934 2,051,912 Smulski Aug. 25, 1936 2,121,607 Mcllvaine June 21, 1938 2,130,829 Ackermann Sept. 20, 1938 2,290,261 Welch July 21, 1942 FOREIGN PATENTS Number Country Date 841,896 France Feb. 20, 1939 

